In U.S. Pat. No. 4,468,623 to Gianzero et al a method and apparatus are described with which fine resistivity measurements are made with an array of small button electrodes. With such array it then becomes possible to obtain a display log as illustrated in and using the techniques described in a copending patent application entitled Method And Apparatus For Producing An Image Log Of A Wall Of A Borehole Penetrating An Earth Formation, filed on Dec. 18, 1984 bearing U.S. Ser. No. 682, 817 by Michael P. Ekstrom et al and assigned to the same assignee as for this application.
In such image log sediment features which are on the scale of millimeters can be observed as illustrated at display log 20 in FIG. 1. Although the display log 20 is effective in providing a fine detailed resistivity presentation of a borehole wall, the expanded scale provides an enormous amount of material for analysis. Hence, techniques are needed to enable an automatic reliable analysis or detection of features of interest. For example, the thickness of beds such as 22, their inclination angle, the frequency of occurrence of the beds may need to be automatically determinable to enable a geologist to select particular regions of interest.
Improvements in an automatic analysis can be obtained by providing clear, relatively noise-free resistivity data. Although the aforementioned copending application describes an invention which is effective in removing noise from the raw electrode data, some noise remains as can be seen, for example, at 24 in the form of vertical streaks and irregular boundaries between beds. It is, therefore, one object of the invention to enhance such fine resistivity measurements to enable their automatic analysis and enhance their visual presentation.